add keywords field detection in ymf

[jerCarre]

Hi,

Because some tools like pandoc use "keywords" field instead of "tags", could you add this field detection in Yaml Front Matter header ?

Thx

[Brend-Smits]

Hey jerCarre,

I will try to add this soon(ish). In the meanwhile you could use some script to detect and convert it yourself :)
Thanks for opening this issue!